Can't expand node from code

Following the Vaadin book I created a tree for my application with the exception that I add Property items instead of strings to wrap some objects I’m putting in the tree. When I try to expand the root node I get a false value. Looking at the tree code that should be because areChildrenAllowed(itemId) is returning false. I’m trying to figure out how to set that to true. Any ideas?

XincoCoreNodeProperty rootProperty = new XincoCoreNodeProperty(xcns);
        //Clear tree and start over
        xincoTree.removeAllItems();
        root = xincoTree.addItem(rootProperty);
       //This adds children from database
        addChildren(rootProperty);
        //Expand root
        xincoTree.expandItem(root);

Here’s the code of the property:

package com.bluecubs.xinco.core.server.vaadin;

import com.bluecubs.xinco.core.server.service.XincoCoreNode;
import com.vaadin.data.Property;

/**
 *
 * @author Javier A. Ortiz Bultrón <javier.ortiz.78@gmail.com>
 */
public class XincoCoreNodeProperty implements Property {

    private XincoCoreNode node = null;

    public XincoCoreNodeProperty(XincoCoreNode node) {
        this.node = node;
    }

    @Override
    public String toString() {
        return node == null ? "Empty" : node.getDesignation();
    }

    @Override
    public Object getValue() {
        return node;
    }

    @Override
    public void setValue(Object newValue) throws ReadOnlyException, ConversionException {
        if (newValue instanceof XincoCoreNode) {
            if (isReadOnly()) {
                throw new ReadOnlyException();
            }
            node = (XincoCoreNode) newValue;
        } else {
            // Don't know how to convert any other types
            throw new ConversionException();
        }
    }

    @Override
    public Class<?> getType() {
        return XincoCoreNode.class;
    }

    @Override
    public boolean isReadOnly() {
        return true;
    }

    @Override
    public void setReadOnly(boolean newStatus) {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

I’m guessing I need to access the Hierarchical container somehow. Any ideas?